Gas-conserving regulators include oxygen regulators, which are used to supply a patient with a regulated flow of oxygen. The oxygen is supplied by a source of compressed oxygen, such as from a supply tank, which has its pressure reduced to a low pressure (e.g., 22 PSI) for delivery to the patient. Typical oxygen regulators employ a back-pressure piston to supply a continuous flow of that low pressure oxygen to the patient. Much of that oxygen is wasted because it is not inhaled by the patient.
To reduce the amount of wasted oxygen, oxygen-conserving regulators have been developed. These regulators tend to limit the oxygen flow to periods of inhalation. The oxygen flow can be controlled electronically or pneumatically.
In pneumatic conserving regulators, a reservoir coupled to the oxygen source holds a supply of oxygen for delivery to the patient. Delivery of the oxygen is controlled by a slave diaphragm that separates the reservoir from a timing gas chamber. The slave diaphragm seals the opening to a delivery nozzle when the patient is not inhaling and releases the seal from the nozzle opening when the patient inhales. The slave diaphragm is made from a flexible material and is generally pressurized toward the closed position. Operation of the slave diaphragm is controlled by a pilot diaphragm, which is coupled to the patient. When the patient inhales, the pilot diaphragm lifts off an orifice pneumatically connected to the timing gas chamber. The oxygen in the timing gas chamber is then expelled, creating a pressure drop sufficient to allow the slave diaphragm to move away from the slave nozzle, thus allowing flow to the patient.
In a dual-lumen conserver (i.e., demand conserver), when the patient stops inhaling—causing the pilot diaphragm to close—the timing chamber builds back to operating pressure (e.g., 22 PSI) almost immediately. Consequently, when the pilot diaphragm shuts against the pilot nozzle, flow to the patient stops. This is usually done by having a preset timing flow between 100 cc and 350 cc per minute, depending on the design of the device. The need to stop flow as soon as the pilot diaphragm closes is because, in a demand conserver, the pilot diaphragm stays open as long as the patient inhales. The dual-lumen design of such conservers allows the unit to be sensitive enough to sense the vacuum caused by inhalation.
A single-lumen conserver does not have that sensitivity, because as soon as the pilot diaphragm opens, the flow of oxygen to the patient overwhelms the device's ability to sense the vacuum caused by the patient during inhalation. In these devices, oxygen is delivered to the patient for an interval of time.